State how Sample was selected

Sample is a statistically valid number taken from the population as bases for the generalization.

Advantages:
1. Less expensive;
2. Shorter period of the conduct of the study and
3. Less effort will be exerted by the researcher it is

because researcher will only be dealing with smaller number of subjects or respondents.

Write up for sample selection mus be based on the:

1. appropriateness in terms of number and source to ensure validity of the study.

2. Biasness must be avoided.
3. specifying the sampling technique used in the study.

Formula (by Slovin, 1960) to get a statistically valid number of sample:

where:

n= sample size
N= population size
e= desired margin of error (for medicinal study .01/for behavioral .05)


One must also select an appropriate sampling technique such as simple random, stratified, cluster and systematic sampling.
Always be reminded that description of the selection of the sample must be clearly written in any research paper.
Sampling procedure must be found in the methodology.


Example  of Research Sample:

1.  Title "Effect of Rice Blast and Sheath Blight on Physical Properties
of Selected Rice Cultivars":

Statement of the research sample selection:

Rice samples from naturally infected panicles, as well as samples
from blast-free panicles of rice cultivar LaGrue were collected by
hand from three producers’ fields in Lodge Corner (two sites) and
Ulm, AR. The samples were analyzed for bulk density (mass per
unit volume) and head rice yield.
Environmental conditions during the 1998 cropping season were
not favorable for blast development in the state of Arkansas. Hence,
only one cultivar and one location were available for sampling. Rough
rice samples from blast-free and naturally infected panicles of rice
cultivar M202 were collected from varietal performance trial plots
in Pocahontas, AR, on September 12, 1998. The design structure
for this varietal performance trial was a randomized complete block
design with four replicates. Blast-free and blast-infected panicles of
M202 were collected by hand and hand-threshed individually. Four
samples (or replicates) of rough rice each weighing ≈300 g from
blast-free and blast-infected panicles were collected. Additionally,
20 blast-free and 20 blast-infected panicles per replicate were collected.
From these panicles, the number of unfilled kernels was
counted to determine the percentage of unfilled kernels per panicle.


2. Title: Possible Role of Human Amniotic Membrane as a Radioprotector of the Gastrointestinal System.

Statement of the research Sample selection:
Sixteen male, International Cancer Research (ICR) strain mice, 3-5 weeks old,
 approximately of the same weight, were acquired
from the Bureau of AnimalIndustry.